Surface treatment of aluminum and its alloys

ABSTRACT

The surface of a piece of aluminum or aluminum alloy is decorated with a novel &#39;&#39;&#39;&#39;lizardskin&#39;&#39;&#39;&#39; appearance by passing an alternating electrolytic current at 5 to 50 volts between said piece used as an electrode, and a second electrode, both electrodes being submerged in an aqueous electrolyte bath containing 0.1 to 20 grams/liter of a suitable acid and 0.1 to 20 grams/liter of a polyfluorinated sulfonate surfactant.

United States Patent [191 Patrie et al.

[451 Aug. 12, 1975 SURFACE TREATMENT OF ALUMINUM AND ITS ALLOYS [75] Inventors: Jos Pattie, Grenoble; Jacques Lefebvre; Francois Allegret, both of Voiron, all of France [73] Assignee: Produits Chimiques Ugine Kuhlmann, Paris, France [22] Filed: July 9, 1974 [21] Appl. No.2 486,741

[30] Foreign Application Priority Data July 13, 1973 France 73.25800 [52] US. Cl. 204/33; 117/49; 148/6.1;

204/58; 204/l29.75; 204/l29.95 [51] Int. Cl. C25D 5/44; C25F 3/04 [58] Field of Search 204/35 N, 56 R, 56 M, 58

[56] References Cited UNITED STATES PATENTS 2,750,337 6/1956 Brown et al. 204/51 2,871,425 l/l959 Burnham 317/230 2,941,930 6/1960 Mostovych et a1. 204/29 3,073,765 1/1963 Adams 204/141 3,755,116 8/1973 Terai et a1. 204/l29.95

OTHER PUBLICATIONS Wemick & Pinner, Surface Treatment & Finishing of Aluminum and its Alloys, Draper, Teddington, England (1964), pp. 34, 372, 374-377.

Primary ExaminerJohn H. Mack Assistant ExaminerAaron Weisstuch Attorney, Agent, or FirmPennie & Edmonds [5 7] ABSTRACT The surface of a piece of aluminum or aluminum alloy is decorated with a novel lizardskin appearance by passing an alternating electrolytic current at 5 to 50 volts between said piece used as an electrode, and a second electrode, both electrodes being submerged in an aqueous electrolyte bath containing 0.1 to 20 grams/liter of a suitable acid and 0.1 to 20 grams/liter of a polyfluorinated sulfonate surfactant.

8 Claims, 1 Drawing Figure PATENTED AUG 1 2l975 Example of a "lizardskin" appearance SURFACE TREATMENT OF ALUMINUM AND ITS ALLOYS BACKGROUND OF THE INVENTION The present invention relates to a novel method for surface treatment of aluminum and aluminum alloys, which method obtains in a simple manner a new decorative effect. This invention relates also to the aluminum objects obtained according to the new method.

Many procedures have been proposed for the purpose of attaining decorative effects on the surface of aluminum or aluminum alloys. Some of these are mecht'nical, among which there may be mentioned engraving, embossing, sanding and calendering. Other decorative treatments are chemical or electrochemical such as exemplified by anodizing, electrolytic polishing and brightening, and various methods of coloration and application of dyes. Still other treatments involve application of a coating, such as a paint or varnish, which can be protective as well as decorative. Researches in the field of electrochemical coloration have provided means for obtaining uniform and reproducible effects permitting a wide choice of colors.

SUMMARY OF THE INVENTION The present invention relates to a simple means of obtaining a novel decorative appearance identified herein as lizardskin, whereby the aluminum or aluminum alloy surface is covered with scales which can be varied in size from about I to mm average diameter. By carefully controlling the electrical and chemical parameters involved, the size and shape of the scales, as well as their depth of color and contrastiness in the photographers sense, can be reproduced at will. A photograph illustrating this new lizardskin appearance is presented in the accompanying FIGURE.

Briefly stated, the method of the present invention comprises placing a piece of aluminum or aluminum alloy as one electrode, together with a second electrode, in an aqueous electrolytic bath containing between 0.1 and grams per liter of a suitable acid and between 0.1 and 20 grams per liter of a polyfluorinated sulfonate surfactant; and passing an alternating electrolytic current of industrial frequency between said electrodes at a potential from about 5 to 50 volts.

The present relates also to pieces of aluminum treated by this method and having the unique lizardskin appearance.

The method of this invention can be used to advantage on objects having a wide range of size and thickness. It is particularly useful in decorating construction sheets for covering walls, ceilings and the like and for finishing foil to be used for wrapping, packaging and similar purposes, and all decorative applications where aluminum sheets or pieces are used.

DETAILED DESCRIPTION Electrolytic installations useful in carrying out the method of this invention are conveniently of the type commonly used for graining aluminum and its alloys, for example in the preparation of lithographic plates. The aqueous bath in which the electrodes are submerged can comprise any suitable acid such as hydrochloric acid, nitric acid, boric acid, fluoboric acid, or any acid which in the conditions of the treatment, does not form on the aluminum piece a protective layer of anodic oxide i.e. any acid or salt which, in the absence of the polyfluorinated surfactant, would give an anodic dissolution. Sulfuric acid and chromic acid are not thus suitable in the compositions of this invention containing also fluorinated surfactants.

The concentration of acid useful in the electrolyte baths of this invention is in the range from 0.1 to 20 grams per liter. When hydrochloric acid is used, the preferred range is from 4 to 10 grams/liter; when nitric acid is used the preferred range is 6 to 10 grams/liter.

Electrolysis is carried out between the aluminum piece to be treated, used as one of the electrodes, and a second electrode which can be inert to the treatment conditions, as exemplarily graphite or stainless steel. Alternatively, the second electrode also can be aluminum or an aluminum alloy identical or similar to that of the first electrode. When both electrodes are similar in this manner, the second electrode also is given a lizardskin appearance on the passage of an alternating current between the electrodes, but the decorative result happens only on the opposite faces of each piece.

The alternating potential used in carrying out the electrolytic treatment of this invention is from 5 to 50 volts, with the frequency of the industrial current used, which may be of 50 or 60 cycles. Higher potentials in the stated range, namely from 30 to 50 volts, have been found to permit more rapid operation and to produce a finer design, i.e. with smaller scales. The lower range of potential, about 5 to 20 volts, on the other hand provides a less deep design but with more contrast, with the lizardskin appearance having larger scales. Contrast is here used in the photographers sense, as indicating coarse or sharp gradations of tone, especially between light and dark areas.

The above generalizations as to effect of voltage are derived from observations made with all other operating parameters being identical for the treatments being compared.

In the same sense, raising the temperature has an effect similar to that of raising the potential, i.e. thee design is achieved more rapidly and is finer and more contrasty. In general, temperatures which are suitable are in the range from 5 to 60C, temperatures from 20 to 50C being most suitable.

The distance between the pair of electrodes in obtaining the lizardskin appearance of this invention can vary widely, being suitably from about 2 to 30 cm; and 5 to 15 cm being preferable.

The current density can generally be from 2 to 10 amperes per square decimeter. However, these values are not absolutely limiting. This density depends, as usual, on the other operating parameters including applied potential, temperature and electrical resistance of the bath. It has been observed that, all other conditions remaining the same, the addition of a surfactant to the acid bath causes a diminution in the current density.

The duration of the treatment is not critical. It has been observed that prolonging the time of treatment produces an increasingly finer, deeper and more contrasty design. Treatment time can exemplarily be from about a half-minute to 10 minutes, but these values are not considered to be absolutely limiting.

With the exception of the polyfluorinated surfactant used in this invention, the parameters used in carrying out this decorative treatment are very similar to those used in the aforementioned electrolytic graining. However, the usual result obtained by the conventional graining procedure is a regular and uniformly fine engraving with a color ranging from white to gray depending on the alloy. In view of this prior experience, it is indeed surprising to find that the presence of a polyfluorinated surfactant according to this invention results in the novel lizardskin appearance.

The polyfluorinated anionic sulfonate surfactant used in this invention is a sulfonic acid, or corresponding water-soluble sulfonate salt, derivative of a polyfluorinated alkyl having from 6 to 18 carbon atoms. The preferred surfactant has the formula C F (CH ),,SO l-l or C F (CH ),,SO M where n is 4 to 14, b is 2 or 4 and M is any cation forming a watersoluble salt, exemplarily sodium, potassium or ammonium.

Acids and salts of the preferred type of surfactant are described in commonly assigned French Pat. No. 1,600,425 filed Apr. 21, 1968. This patent combined with French Pat. No. 1,561,360 filed Jan. 31, 1968, both patents having the same inventive entity, discloses exemplary methods of preparing such surfactants whereby the following successive reactions take place, wherein R, represents the perfluoroalkyl group C,,F and X represents a halogen, exemplarily iodine or chlorine and b is 2 or 4:

products Corresponding water-soluble salts are made by the conventional steps of neutralization with an appropriate base.

The perfluorinated alkyl group used in preparing the preferred surfactant can be any straight-chain, branched or cyclic alkyl group having from 4 to 14 carbon atoms and having substantially all of its hydrogens replaced by fluorine. Exemplarily, said alkyl group can be nonafluoro-n-butyl, nonafluoro-isobutyl, nonafluoro-secondary butyl, nonafluorotertiary butyl, undecafluoro-n-amyl, undecafluoro-isoamyl, undecafluoro-tertiary amyl, tridecafiuoro-n-hexyl, undecafluorocyclohexyl, pentadecafluoroheptyl, heptadecafluoro-octyl, heptadecafluoro-2-ethyl hexyl, nonadecafluorononyl, perfluorodecyl (C F perfluoroundecyl (C F perfluorolauryl (C F perfluorotridecyl (C and perfluoromyristyl (C F The preferred perfluoroalkyl group R; is tridecafluoro-nhexyl.

It is preferable that the aluminum or aluminum alloy objects to be treated by the method of this invention should be submitted to a preliminary degreasing to remove industrial forming oils which are usually found remaining on the metal. For this purpose, the conventional solvents and/or detergents can be used. The method of this invention can be applied satisfactorily on substrates which have had such a simple degreasing. The degree of cleaning necessary for a particular commercial batch of substrate material can be evaluated by preliminary experiments. In some cases, as in Example 12 below, material whose past history is not completely known may be used directly without further cleaning.

It is also possible in practice to precede the treatment of this invention with a conventional surface preparation such as chemical polishing, glazing or lustering in order to present a uniform surface for acceptance of the lizardskin treatment.

The surface of aluminum, or an aluminum alloy, which has been given the characteristic lizardskin decoration of this invention can be submitted to an anodization without destroying the lizardskin design. The lizardskin surface can also be protected by the application of a clear varnish. Such after-treatments can be non-colored as in the case of an anodization without dyestuff or the application of a non-colored varnish. Alternatively, the after-treatment can also include a coloring component and/or step, such as a conventional chemical or electrochemical treatment changing the color of the surface. Such a coloring step can be preceded by a non-coloring anodization step. Also, transparent varnishes containing colored materials can be applied.

The invention will be further illustrated by description in connection with the following specific examples of the practice of it, the proportions here and elsewhere herein being expressed in parts by weight unless specifically stated to the contrary.

EXAMPLE 1 20C; current density was fixed at 1.2 amperes per square decimeter of the plate. After treatment for 1 minute, the plate was washed with water and allowed to dry.

There was obtained an effect of light gray lizardskin with little contrast.

EXAMPLE 2 The procedure of Example 1 was repeated except that the bath contained 8 grams/liter of hydrochloric acid (HCl) instead of the nitric acid and the current density was changed to 2.4 amperes per square decimeter. An analogous effect was obtained as in Example 1 except that the contrast was a little more marked.

EXAMPLE 3 The same conditions as in Example 2 were used except that the temperature was 30C and the current density was 2.5 amperes per square decimeter. The attained effect was similar to that of Examples 1 and 2 except that the color was in general a little darker and had more contrast; the scales of the lizardskin had a somewhat larger individual surface.

EXAMPLE 4 The same conditions as in Example 2 were used except that the temperature was 40C and the current density was 2.6 amperes per square decimeter. The effect was very similar to that of Example 2; the scales, however, were more marked.

EXAMPLE 5 The same conditions as in Example 2 were used except that the plate was an alloy of aluminum containing 0.6 of magnesium'and the applied potential was 15 The bath was an aqueous hydrochloric acid solution containing 4.4 grams/liter of HCl and] gram/liter of c m cu cn so n. The plateto be treated and the other electrode were both made from aluminum designated as type A in French practice, i.e. an aluminum of purity at least equal to 99.5 Al. The applied alternating potential was 18 volts of 50 cycles frequency, the temperature was C, the current density was 3.8 amperes/dm The appearance obtained was of very light gray tint with very small scales.

EXAMPLE 8 A plate of aluminum alloy containing 1 manganese was subjected successively to two operations according to this invention. The first was carried out in a bath containing 7 grams/liter of nitric acid HNO and l gram/liter of C F CH CH SO H with the second electrode being of graphite. Applied potential was volts, bath temperature was 20C, current density was 1.2 amperes/dm the treatment lasted seconds.

After washing and rinsing, the same plate was placed in a hydrochloric acid bath containing 8 grams/liter of HCl and 1 gram/liter of C F, Cl-I CH SO H. The second electrode again was graphite. The alternating current was applied at a potential of 10 volts, the temperature was 30C, current density was 2.5 amperesldm the duration of the treatment was for 1 minute.

The surface of the plate after this dual treatment had a relatively dark appearance with scales of large individual area. The result is more contrasted that the result obtained with a treatment in HCl alone with a corresponding duration (l-5 minutes).

EXAMPLE 9 The same conditions were used as in Example 7, except that the current was passed for an extended period of 4 minutes. After washing and rinsing, the plate was anodized by conventional anodizing techniques to a thickness of 9 microns in a sulfuric acid bath of 200 i 10 gram/liter of H 50 at 20C with a current density of 1,5 A/dm then dyed black in a bath containing nickel by the procedure described in the French Pat. No. 2,142,828. There was obtained a black colored plate on which the most brilliant points of the lizardskin configuration were distinguishable in the ground coat.

EXAMPLE 10 A plate obtained according to the procedure of Example 7 was covered with a clear varnish. ltwas observed that the appearance obtained according to this invention was not modified by the varnish.

C1-l C1-1 SO 1-l is substituted successively by 0.1 gram/- EXAMPLE ii Aplate obtained according to the procedure of Example '7 was anodized-to a thickness of 9 microns. A more deeply colored appearance was obtained than in Example-7,apparently witha reinforcement-of the darker parts-"of the lizardskinconfiguration.

EXAMPLE 12 Usingan electrolytic cell capable of accomodating a sheet '2 X 1 meters in area, the cell was filled with an aqueous hydrochloric acid solution containing 8 gram/- liter of HCl and l gramfliter of C FQCH CH SO 'H. A sheet of the stated size, made of an aluminum-alloy containing 1 of manganese, wasus'ed as one electrode, the other electrode being a series of graphite bars. Treatment for a period of 2 minutes was carried out with an alternating current of 50 cycles frequency, having a current density equal to 3.8 amperes per dm at a potential of 10 volts. The temperature was maintained at 30C.

It is noteworthy that the sheet used for this treatment was not submitted to preliminary degreasing or clean- EXAMPLE 13 Equipment was used permitting continuous unwinding of bands of aluminum 400 mm. wide. The metal bands passed successively through (1) a compartment in which they were degreased by a spray, and (2) an electrolytic cell 3.45 meters long. The bath had the same composition as in Example 2, except that the potential was 15 volts and the temperature was 14C. Current density was 2.7 amperes per square decimeter.

The moving band acting as one of the electrodes in this example had a thickness of 0.8 mm, was made of an aluminum alloy containing 1 of manganese, and moved at a rate of 3 meters/minute while the other electrode, a series of graphite bars, remained in place.

The resulting surface had a light-gray appearance with lizardskin scales having a generally large individual area.

EXAMPLE 1 4 The procedure of Example 13 is repeated except that in place of the inert graphite bars, a second moving aluminum band is used, travelling at the same speed. Both bands of aluminum are given a similar lizardskin appearance on the faces of the bands which are opposite.

EXAMPLE 15 The procedure of Example 2 is followed in a series of 24 experiments in which the 1 gram/liter of C 1 liter, 1 gram/liter, 1O gram/liter and 20 gram/liter respectively of each of the following substances:

nC F -CH Ch SO H 3--C F -CH CH SO l-l nC F13CH2SO3H I nC F 3CH2CH2SO3Na In each case a lizardskin appearance according to this invention is given to the metal surface.

What is claimed is:

l. A method of decorating the surface of a piece of aluminum or aluminum alloy with a lizardskin appearance, which method comprises placing said piece as one electrode together with a second electrode in an aqueous electrolytic bath at about 60C and containing from about 0.1 to grams/liter of hydrochloric acid, nitric acid, boric acid or fluoroboric acid and from about 0.1 to 20 grams/liter of a polyfluorinated sulfonate surfactant; and passing an alternating electrolytic current of 5060 cycles between said electrodes at a potential from about 5 to 50 volts.

2. The method of claim 1 wherein the polyfluorinated sulfonate surfactant is C F (Cl-l SO Q, wherein n is 4 to 14, b is 2 or 4, and Q is H or any cation forming a water-soluble salt.

3. The method of claim 2 wherein the surfactant is Z-(tridecafluoro-n-hexyl)-ethyl' sulfonic acid.

4. The method of claim 1 wherein the second electrode is an inert material.

5. The method of claim 1 wherein the second electrode also is a piece of aluminum or aluminum alloy, whereby the opposite surfaces of both electrodes are decorated with the lizardskin appearance.

6. The method of claim 1 wherein the lizardskin surface is subsequently protected by anodization or the application of a clear varnish.

7. The method of claim 1 wherein the lizardskin surface issubsequently colored. w

8. A piece of aluminum or aluminum alloy whose surface is decorated by the method of claim 1.

UNITED TTATTT PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,899,400

DATED August 12, 1975 N E M Jos Patrie, Jacques Lefebvre and Francois Allegret It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

1. In Column 2, line 39, "thee" should read the--.

2. In Column 5, line 47, "(l5 minutes)" should read (1.5 minute).

Signed and Scaled this twenty-first D 21) Of October 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'Patents and Trademarks 

1. A METHOD OF DECORATING THE SURFACE OF A PIECE OF ALUMINUM OR ALUMINUM ALLOY WITH A "LIZARDSKIN" APPEARANCE, WHICH METHOD COMPRISES PLACING SAID PIECE AS ONE ELECTRODE TOGETHER WITH A SECOND ELECTRODE IN AN AQUEOUS ELECTROLYTIC BATH AT ABOUT 5*-60*C AND CONTAINING FROM ABOUT 0.1 TO 20 GRAMS/LITER OF HYDROCHLORIDE ACID, NITRIC ACID, BORIC ACID OR FLUOROBORIC ACID AND FROM ABOUT 0.1 TO 20 GRAMS/LITER OF A POLYFLUORINATED SULFONATE SULFACTANT, AND PASSING AN ALTERNATING ELECTROLYTIC
 2. The method of claim 1 wherein the polyfluorinated sulfonate surfactant is CnF2n 1(CH2)bSO3Q, wherein n is 4 to 14, b is 2 or 4, and Q is H or any cation forming a water-soluble salt.
 3. The method of claim 2 wherein the surfactant is 2-(tridecafluoro-n-hexyl)-ethyl sulfonic acid.
 4. The method of claim 1 wherein the second electrode is an inert material.
 5. The method of claim 1 wherein the second electrode also is a piece of aluminum or aluminum alloy, whereby the opposite surfaces of both electrodes are decorated with the lizardskin appearance.
 6. The method of claim 1 wherein the lizardskin surface is subsequently protected by anodization or the application of a clear varnish.
 7. The method of claim 1 wherein the lizardskin surface is subsequently colored.
 8. A piece of aluminum or aluminum alloy whose surface is decorated by the method of claim
 1. 